1. Field of the Invention
The present invention relates generally to voltage regulators, and more particularly, to a voltage and current regulator having switchable voltage-sensitive elements which respond to variations in the potential difference appearing across two reference terminals and serve to positively turn on and turn off a power transistor or the like.
2. Description of the Prior Art
A voltage regulator is generally employed in a generating circuit to limit the generator voltage and current to predetermined values by controlling the generator field current.
Heretofore, voltage regulators for use in generating systems typically include a power transistor or the like, which when conductive permits current to flow in a field winding of a generator. In one type of regulator a second transistor is connected with its collector-emitter path across the base-emitter path of the power transistor and with its collector connected to the base of the power transistor and to a reference voltage supplying conductor through an arrangement of bias resistors. The conduction of the second transistor is controlled by voltage sensitive means in its base circuit that respond to the potential difference across two reference terminals of the regulator. However, in order to turn off the power transistor, the second transistor is required to supply a relatively high current through the bias resistors, and hence a corresponding high voltage, to the base of the power transistor before the bias voltage developed is able to cause the power transistor to stop conducting. As a result, the power transistor is slow to turn off in response to substantial increases in the potential difference appearing across the reference terminals. In addition, substantial currents flow through the bias resistors when the power transistor is turned off, resulting in a substantial power loss and heat production in the circuit.
An example of such a voltage regulator is found in U.S. Pat. No. 3,593,113, entitled "Voltage Regulators Using Plannar Transistors With Radio Interference Suppression," by David Wiley.